Dilute cleaning composition and method for using same

ABSTRACT

A cleaning method in a semiconductor fabrication process includes providing a dilute composition consisting essentially of phosphoric acid and acetic acid and exposing a surface, e.g., aluminum, to the dilute composition. For example, the dilute composition includes phosphoric acid at a concentration of about 5% or less by volume and acetic acid at a concentration of about 30% or less by volume. Further, the cleaning method may use a composition comprising phosphoric acid and acetic acid, wherein the composition includes phosphoric acid at a concentration of X %, wherein X is about 5% by volume or less, and acetic acid at a concentration of about (100-X %) by volume or less. The cleaning method may be used, for example, in fabricating interconnect structures, aluminum containing structures, and multilevel interconnect structures. Cleaning compositions for use in the cleaning methods are also provided.

REFERENCE TO CROSS-RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/325,375 filed Jun. 4, 1999 which is a continuation in part of U.S.patent application Ser. No. 08/808,014 filed Mar. 3, 1997, incorporatedherein by reference thereto.

FIELD OF THE INVENTION

The present invention relates to the fabrication of semiconductorintegrated circuits, and in particular, to cleaning compositions andmethods for cleaning surfaces during fabrication.

BACKGROUND OF THE INVENTION

In the fabrication of semiconductor integrated circuits (ICs), activedevice regions are formed in semiconductor substrates, isolated fromadjacent devices with an isolating material. Electrical paths connectsuch active devices, using thin-film structures, such as metallines/patterned metal layers. Such structures make contact with activedevices through openings, or contact holes, in the isolating material.One primary concern in forming such interconnects is the maintenance ofa low level of resistivity throughout an IC in order to ensure devicesperform properly. As ICs are scaled down in size, so are the deviceswhich make up the ICs. Increases in resistance are associated withincreasing circuit density and adversely affect device performance,slowing them down and increasing power consumption. Thus, ways todecrease the overall resistance of ICs are crucial to continuedsuccessful device performance.

In many applications, the metal lines/patterned metal layers are formedon a different level than the active devices, separated by an insulatinglayer, such as, for example, silicon dioxide or borophosphosilicateglass (BPSG). Furthermore, there may be more than one level of metallines/patterned metal layers, connected by conductive interconnectsformed in vias defined in an insulating layer between adjacent metallines/patterned metal layers. Commonly used metal lines/patterned metallayers include aluminum, to which copper may be added to form an alloy.Interconnects are also formed between individual devices and the metallines/patterned metal layers. A typical interconnect to an active deviceregion is formed in a contact hole defined in an insulating layer overthe active device region. The contact hole is filled with one or moremetals, such as, for example, aluminum or tungsten.

In lowering resistivity of an IC, it is important to remove all foreignresidue from interfaces in the IC. As multiple layers are formed in ICs,individual layers may need to be cleaned before the next layer is formedor before surface modification is done. Numerous preclean proceduresexist for use prior to semiconductor surface modification in batchfurnaces, including wet chemical cleans, hydrogen bakes, phosphoricacid, and hydrofluoric acid (HF) vapor cleans. Many cleaningcompositions undesirably contain strong, i.e., not dilute, organicsolvents, which typically are disposed of using special hazardous wastedisposal techniques.

Preclean procedures are important to both reduce native oxide and removeother contaminants, such as, for example, residual organic and metallicimpurities. Residual photoresist and other organic materials used inprocessing steps, such as, for example, etches, are often hard to removefrom surfaces during IC fabrication. In particular, such residualmaterials are hard to remove from metal surfaces and surfaces adjacentto metal layers due to the metallization of such organic residue on thesurfaces, particularly as a result of intermixing of materials duringetch steps. Thus, metal layers and vias have been hard to effectivelyclean in the past after completion of patterning etches and via etchesthrough insulating layers thereon. Further, conventional cleaningcompositions used are typically hazardous and require special handlingand disposal procedures.

Therefore, for the reasons as described above, there is a need foreffective cleaning compositions and methods of cleaning surfaces duringfabrication of ICs. For example, a composition and method for cleaningmetal surfaces during fabrication is needed to remove metallized organicresidue from surfaces during IC fabrication in order to lower theresistivity of resulting ICs. Further, it is desirable that the cleaningcompositions utilized can be disposed of safely and easily.

SUMMARY OF THE INVENTION

A cleaning method in a semiconductor fabrication process according tothe present invention includes providing a dilute composition consistingessentially of phosphoric acid and acetic acid and exposing a surface tothe dilute composition. In one embodiment of the method, the dilutecomposition includes phosphoric acid at a concentration of about 5% orless by volume and acetic acid at a concentration of about 30% or lessby volume. More preferably, in one embodiment of the dilute composition,the dilute composition includes phosphoric acid at a concentration ofabout 5% or less by volume and acetic acid at a concentration of about10% or less by volume. In another embodiment, the dilute compositionincludes phosphoric acid at a concentration of about 5% or less byvolume and acetic acid at a concentration in the range of about 20% byvolume to about 30% by volume.

Another cleaning method according to the present invention includesproviding a composition comprising phosphoric acid and acetic acid,wherein the composition includes phosphoric acid at a concentration of X%, wherein X is about 5% by volume or less, and acetic acid at aconcentration of about (100-X %) by volume or less. A surface is thenexposed to the composition. In one embodiment of the method, thecomposition is a dilute composition, wherein the dilute compositionincludes phosphoric acid at a concentration of about 5% by volume orless, acetic acid at a concentration of about 30% by volume or less, anddeionized water. In another embodiment, the surface is of a conductivelayer.

A method of fabricating an interconnect structure according to thepresent invention is also provided. The method includes patterning aconductive layer and cleaning the conductive layer using a compositioncomprising phosphoric acid and acetic acid. The composition includesphosphoric acid at a concentration of about X % or less by volume, whereX is 5, and acetic acid at a concentration of about (100-X) % or less byvolume. In one embodiment of the method, the composition is a dilutecomposition, and further, the dilute composition includes phosphoricacid at a concentration of about 5% or less by volume and acetic acid ata concentration of about 30% or less by volume. In another embodiment,the dilute composition includes phosphoric acid at a concentration ofabout 5% or less by volume and acetic acid at a concentration of about10% or less by volume.

In another embodiment of the method, the conductive layer comprisesaluminum. Further, the patterning may include patterning the aluminumlayer using a chlorine-containing etchant and a photoresist whichresults in organic residue on at least a part of the conductive layer.The cleaning then removes the organic residue, e.g. a metallized organicresidue.

In addition, a method of fabricating a multilevel interconnect structureis described. The method includes providing an insulating layer over afirst metal layer. A via is defined in the insulating layer resulting inresidue on an exposed portion of the first metal layer. The residue isremoved using a dilute cleaning composition consisting essentially ofphosphoric acid and acetic acid. The dilute cleaning compositionincludes phosphoric acid at a concentration of about 5% or less byvolume and acetic acid at a concentration in the range of about 20% byvolume to about 30% by volume.

Yet another method according to the present invention includes providinga structure including an aluminum containing conductive region andproviding a dilute composition consisting essentially of phosphoricacid, acetic acid, and deionized water. The structure is then exposed tothe dilute composition to clean at least the aluminum containingconductive region. Preferably, the dilute composition includesphosphoric acid at a concentration of about 5% or less by volume and theacetic acid at a concentration of about 30% or less by volume.

In various embodiments of the above methods, the surface is of aconductive layer. Preferably, when exposing the conductive layer to thecomposition, etching of the conductive layer occurs at a rate of lessthan about 200 Å/minute. More preferably, such etching of the conductivelayer occurs at a rate of less than about 50 Å/minute. Further,preferably, etching of the conductive layer occurs such that less thanabout 500 Å of conductive material is removed from the conductive layerduring an exposure period of less than 10 minutes; preferably, less thanabout 200 Å during an exposure period of less than 10 minutes; morepreferably, less than about 50 Å during an exposure period of less than10 minutes.

A cleaning composition for use in semiconductor integrated circuitfabrication according to the present invention consists essentially of adilute aqueous solution of phosphoric acid and acetic acid. Thephosphoric acid is of a concentration of about 5% by volume or less andthe acetic acid is of a concentration of about 30% by volume or less.Preferably, in one embodiment, the phosphoric acid is of a concentrationof about 5% or less by volume and the acetic acid of a concentration ofabout 10% or less by volume. In another embodiment, the phosphoric acidis of a concentration of about 5% or less by volume and the acetic acidis of a concentration in the range of about 20% by volume to about 30%by volume.

Another cleaning composition for use in semiconductor integrated circuitfabrication according to the present invention includes phosphoric acidand acetic acid. The composition includes phosphoric acid at aconcentration of about X % by volume or less, where X is 5, and aceticacid at a concentration of about (100-X) % by volume or less. In oneembodiment, the composition is a dilute composition, wherein the dilutecomposition includes phosphoric acid at a concentration of about 5% byvolume or less, acetic acid at a concentration of about 30% by volume orless, and deionized water.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1A to 1K are cross-sectional representations of a multilevelinterconnect structure formed using a cleaning composition includingphosphoric acid and acetic acid in accordance with the presentinvention, and intermediate structures thereof.

DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying Figures which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that changesmay be made without departing from the scope of the present invention asdefined in the accompanying claims. For example, the terms wafer andsubstrate used herein include any semiconductor-based structure. Bothare to be understood as including silicon-on-sapphire (SOS) technology,silicon-on-insulator (SOI) technology, doped and undoped semiconductors,epitaxial layers of silicon supported by a base semiconductor, as wellas other semiconductor-based structures well known to one skilled in theart. Furthermore, when reference is made to a wafer or substrate in thefollowing description, previous process steps may have been utilized toform regions/junctions in the semiconductor-based structure previouslyformed. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims.

Generally, a chemical composition in accordance with the presentinvention for use in wet cleans in semiconductor processing includesboth phosphoric acid and acetic acid. The chemical compositionpreferably includes about 5% by volume or less of phosphoric acid withthe remaining portion of the composition being acetic acid or with theremaining portion being acetic acid and deionized water. In other words,the composition includes about X % by volume or less of phosphoric acidand about (100-X) % by volume or less of acetic acid, where X is 5. Thischemical composition provides better solvation of metallized polymersand organic polymers than previously used cleaning compositions, such asstandard phosphoric acid cleans. However, the chemical compositionprevents removal of too much material from the surface being cleaned,e.g., an aluminum containing surface. The use of both acidic componentstogether in the cleaning composition is beneficial. The phosphoric acidcomponent promotes solvation of inorganic residue, while the acetic acidcomponent promotes salvation of organic residue. Further, andsurprisingly, acetic acid passivates a metal containing surface beingcleaned, e.g., patterned aluminum, so as to prevent undesirable removalof substantial amounts of the metal by the phosphoric acid during thecleaning process.

Preferably, the chemical composition is a dilute composition. Diluterefers to a composition having about 35% reactive components or less byvolume. The dilute chemical composition is advantageous as compared withpreviously used strong (i.e., not dilute) solution cleans because itdoes not require special hazardous waste disposal. Acetic acid is a mildorganic reactant and the concentration at which it is preferably used inthe preferred dilute compositions according to the present invention issafe and would generally not require the use of special exhaust hoods(e.g., VOC hoods) when used to perform a cleaning operation. Preferably,the concentration of phosphoric acid in the dilute chemical compositionis about 5% by volume or less. The concentration of acetic acid in thedilute solution is about 30% by volume or less. The wet etch using thedilute composition is generally performed over a certain time period,e.g., the time period during which the structure being cleaned isimmersed in the dilute solution. Preferably, this time period is in therange of about 15 seconds to about 10 minutes. More preferably, the timeperiod is in the range of about 15 seconds to 5 minutes, and yet morepreferably in the range of about 15 seconds to 90 seconds.

Different preferred chemical concentrations for the dilute compositionincluding phosphoric acid and acetic acid may be used depending upon thestructure to be cleaned. With respect to patterned metal surfaces, e.g.,patterned aluminum layers, to be cleaned, preferably, the concentrationof phosphoric acid in the dilute chemical composition is about 5% byvolume or less. The concentration of acetic acid in the dilute solutionis preferably about 30% by volume or less; more preferably about 10% byvolume or less. The reactive components are diluted in any suitablesolvent, preferably, deionized water. If the concentration of thephosphoric acid component is increased above 5%, excess metal loss mayundesirably result from the surface being cleaned. The concentration ofthe two acidic components is such that effective removal of residue on asurface, particularly metallized organic residue, is accomplished. Asused herein, patterned metal surfaces refers to surfaces of structuresthat do not include an opening defined therein which exposes anunderlying metal layer, e.g., oxide layers patterned with vias to exposeun underlying metal layer. Preferably, the structure including thepatterned metal surfaces is immersed in the dilute composition for about15 seconds to about 90 seconds, although the structure may be immersedin the dilute composition for longer times.

With respect to etched openings and/or metal surfaces at the bottom ofsuch openings (e.g., aluminum at the bottom of a via of an interconnectsystem, metal in a contact opening, etc.), preferably, the concentrationof phosphoric acid in the dilute chemical composition is about 5% byvolume or less. The concentration of acetic acid in the dilute solutionis in the range of about 20% by volume to about 30% by volume. Thereactive components are diluted in any suitable solvent, preferably indeionized water. Again, if the concentration of the phosphoric acidcomponent is increased above 5%, excess metal loss may undesirablyresult from the surface being cleaned. Preferably, the structureincluding the etched openings is immersed in the dilute composition fora time period of about 15 seconds to about 90 seconds. More preferably,the structure is immersed in the dilute composition for about 30seconds.

Although different concentrations of acidic components may be used inthe dilute compositions for different cleaning applications, preferablythe dilute composition is such that when used to clean surfaces havingexposed metals, e.g., aluminum, less than 500 Å of the metal is removedduring the cleaning process. More preferably, less than 200 Å of theexposed metal is removed, and further, yet more preferably, less than 50Å of the exposed metal is removed. The wet etch rate for the metalduring the clean is preferably less than about 200 Å/minute, morepreferably less than about 50 Å/minute.

Preferably, the chemical composition is heated above ambient temperaturein a circulating bath prior to its use. The chemical composition isheated to about 50 degrees Celsius or less. If higher temperatures areused, the integrity of underlying metallic layers is possibly degraded.Preferably, temperatures of about 30 to about 45 degrees Celsius areused for optimizing the cleaning abilities without severe metal lossfrom underlying layers when the concentration of the phosphoric acidcomponent present in the composition is of an amount of about 5% or lessby volume. When lower concentrations of the phosphoric acid componentare present in the composition, higher temperatures may be effectivelyused without severe metal loss from underlying layers. Similarly, whenhigher concentrations of the phosphoric acid component are present inthe composition, lower temperatures may need to be used to avoid severemetal loss from underlying layers.

The chemical composition of the present invention is typically used forcleans performed in the fabrication of an interconnect structure. Forexample, the present invention is useful for cleans performed infabricating a multilevel interconnect structure. Interconnect structure,as used herein, refers to vias, contacts, metal lines/patterned layers,pads, and similar conductive circuitry utilized in an integratedcircuit. FIGS. 1A to 1K illustrate a multilevel interconnect structureand intermediate structures thereof. Dimensions and scaling in theFigures are not exact, but represent the nature of fabricating amultilevel interconnect structure in general and the necessity forutilizing the chemical composition of the present invention for cleaningintermediate structures thereof.

In the fabrication of a multilevel interconnect structure, a contacthole 18 is typically defined in an insulating layer 20, such as, forexample, borophosphosilicate glass (BPSG), as illustrated in FIG. 1A.The contact hole 18 is defined over an active area of an underlyingsubstrate, as represented generally by 22. An interconnect structure 24is then formed in the contact hole 18 using any suitable materials andmethods for forming the same. Typical interconnect 24 fabricationincludes formation of a series of layers, such as, for example, titaniumsilicide, titanium nitride, and a metal plug or other conductive layers.Next, a blanket layer of metal 26 is deposited over the interconnectstructure 24 and insulating layer 20, to produce the structureillustrated in FIG. 1A. The metal layer 26 can be any conductivematerial, such as, for example, aluminum or aluminum alloyed withcopper. Other elements that can constitute the conductive materialinclude titanium and silicon.

A photoresist layer 28 is then deposited on the metal layer 26 andpatterned as well known to one skilled in the art, resulting in thestructure illustrated in FIG. 1B. The metal layer 26 is then etched inexposed areas, resulting in the metal line structure illustrated in FIG.1C.

The etchant used to pattern the metal layer 26 varies. For patterningaluminum, chlorine-containing etchants are typically used, i.e., forexample, Cl₂, BCl₃, CCl₄, SiCl₄ and combinations thereof. However, theexact nature of the etchant is not critical to the scope of theinvention.

Residue 29, such as organic residue of etch-related polymers, oftenremains on the exposed metal 26 surface. Depending on the constituentelements of the exposed metal surface 26, the etchant, and theetch-related polymers, the chemical nature of the residue 29 varies. Forexample, titanium, aluminum, copper, and silicon are common elementsutilized in semiconductor fabrication. Carbon, chlorine, and fluorineare common elements utilized in etchants. Carbon and nitrogen are commonelements present in etch-related polymers. These elements, orcombinations thereof, are typically found in residue 29 on such surfaces26. Furthermore, oxygen may be present in the residue 29 as a result ofthe etch-related polymer stripping, for example, when using an oxygenash for removal of photoresist. In particular, when the etchant containschlorine, the organic residue often includes aluminum chloride or copperchloride, for example, when the exposed metal 26 surface is aluminum oraluminum alloyed with copper.

In order to prepare the surface of the structure illustrated in FIG. 1Cfor insulating layer deposition, the photoresist layer 28 is nextremoved. To remove the photoresist layer 28 and/or other etch-relatedpolymers after patterning the first metal layer 26, an oxygen ash iscommonly used, or any suitable method (wet or dry), as well known to oneskilled in the art. For example, a typical oxygen ash includes heatingthe structure in a process chamber having a temperature of about 200 to300 degrees Celsius and in the presence of an oxygen-containing plasma.Other examples include heating the structure in the presence of anozone-containing environment or wet cleaning the structure using organicstrippers.

Even after the oxygen ash step, residue 29, such as organic componentsfrom the photoresist 28 often remain on the first metal layer 26, asillustrated in FIG. 1D. If not removed, such residue 29 increases theresistivity of the interconnect structure, degrading electricalperformance. The longer the first metal layer 26 is exposed to thephotoresist 28 during the etch process, the harder it becomes toeffectively remove all of the residue 29, such as organic residue, fromthe surface of the first metal layer 26. This is due to the fact thatthe organic materials become metallized, as previously mentioned. Thus,the structure illustrated in FIG. 1D is exposed to the cleaningcomposition of this invention after the oxygen ash step. The exposuretime needed for effectively cleaning the metallized organic residue 29varies. The exposure time is adjusted to allow for adequate cleaningwithout removing excess metal from underlying surfaces. As one example,an exposure time of about 90 seconds seems to provide an adequatebalance between these two competing factors, such as, for example, whenusing concentrations of about 10% by volume of acetic acid in additionto about 5% by volume of phosphoric acid and temperatures of about 30 toabout 45 degrees Celsius. The cleaning composition of this invention ismore effective than conventionally used standard phosphoric acidcompositions at removing such residue 29, including any metallizedorganic elements, due to the acetic acid component passivating the metalsurfaces preventing over etching of the metal during the clean.

After the first metal layer 26 is patterned and cleaned with thechemical composition of this invention, an insulating layer 30 is formedover the first metal layer 26, as illustrated in FIG. 1E. The insulatinglayer 30 can be any dielectric material, such as, for example, silicondioxide, spin-on-glass, or borophosphosilicate glass. Typically, theinsulating layer 30 has a low dielectric constant and is formed atrelatively low temperatures. Silicon dioxide may be used for theinsulating layer 30. The silicon dioxide 30 is formed using any wellknown technique, such as, for example, tetraethyloxysilicate(TEOS)-based plasma-enhanced chemical vapor deposition (PECVD). Thethickness of the insulating layer 30 is determined according to thefeature sizes of the integrated circuit as well known to one skilled inthe art.

To define a via in the insulating layer 30, a photoresist layer 28 ispatterned over the insulating layer 30, as illustrated in FIG. 1E. Thevia 32 is then defined in the exposed portions of the insulating layer30 by etching away the exposed insulating layer 30, the resultingstructure of which is illustrated in FIG. 1F. The etchant used to definethe via 32 varies. Typical etches often comprise more than one step. Forexample, to define a via 32, a wet etch at standard temperature may befollowed by a dry etch (i.e., plasma etch), two adjacent dry etches maybe used instead, or a single dry etch may also be used.

For etching silicon dioxide, plasma etchants often contain a fluorinecomponent. Typical etchants include, but are not limited to, CF₄, C₂F₆,C₃F₈, CHF₃, NF₃, SF₆ and combinations thereof Once again, residue 29,such as organic residue of etch-related polymers, often remains on theexposed metal 26 surface. As previously described, however, the chemicalnature of such residue 29 varies depending on the constituent elementsof the exposed metal surface 26, the etchant, and the etch-relatedpolymers. In particular, when the etchant contains fluorine, the residue29 often includes metal fluorides, such as, for example, aluminumfluoride, if the exposed metal 26 is aluminum.

In order to prepare the surface for the next metal layer deposition, thephotoresist layer 28 is removed, resulting in the structure illustratedin FIG. 1G. To remove the photoresist layer 28 and/or etch-relatedpolymers after defining the via 32, an oxygen ash, or any suitablemethod, is commonly used, as described previously.

After the oxygen ash step, residue 29, such as organic components fromthe photoresist 28 often remain on the first metal layer 26 at thebottom of the via and on the sidewalls of the via 32 at the insulatinglayer 30 interface. The longer the first metal layer 26 is exposed atthe bottom of the via 32, the harder it becomes to effectively removeall of the residue 29 at the bottom of the via 32. This is due to thefact that the organic materials become metallized, as previouslydescribed. Thus, the structure illustrated in FIG. 1G is exposed to thecleaning composition of this invention after the oxygen ash step.

The exposure time needed for effectively cleaning the metallized organicresidue 29 varies. The exposure time must be adjusted to allow foradequate cleaning without removing excess metal from underlyingsurfaces. As one example, an exposure time of about 30 seconds using adilute solution of about 25% by volume of acetic acid and 5% by volumeof phosphoric acid seems to provide an adequate balance between thesetwo competing factors.

The cleaning composition of this invention is more effective thanconventionally used phosphoric acid compositions at removing suchresidue 29. However, while piranha cleans (i.e. mixtures of hydrogenperoxide and sulfuric acid) are used for cleaning contact holes, theycannot be used for cleaning vias 32 and metallic surfaces 26, due totheir extreme reactivity. The extreme reactivity of such conventionalcleans results in severe metal loss from exposed metal surfaces.

Next, as illustrated in FIG. 1H, an interconnect structure 34 is formedin the via 32 and a second metal layer 36 is formed over the insulatinglayer 30 and structure 34. The second metal layer 36, like the firstmetal layer 26 and any subsequent metal layers, can be any conductivematerial, such as, for example, aluminum or aluminum alloyed withcopper. Furthermore, the conductive material constituents can includetitanium and/or silicon. The second metal layer 36 is then patterned, aswell known to one skilled in the art. A patterned photoresist layer 28is formed over the second metal layer 36, as illustrated in FIG. 1H. Thesecond metal layer 36 is then etched in exposed areas, the resultingstructure of which is illustrated in FIG. 1I. The resulting structureoften undesirably contains residue 29, such as organic residue, on theexposed surfaces of the second metal layer 36. The etchant used topattern the second metal layer 36 varies, as described previously,contributing to the presence of the residue 29 on the metal surfaces.

In order to prepare the surface of the structure illustrated in FIG. 1Ifor deposition of subsequent layers, the photoresist layer 28 is nextremoved. To remove the photoresist layer 28 and/or etch-related polymersafter patterning the second metal layer 36, an oxygen ash, or anysuitable method, is commonly used, as described previously.

After the oxygen ash step, residue 29, such as organic components fromthe photoresist 28, often remain on the second metal layer 36, asillustrated in FIG. 1J. The longer the second metal layer 36 is exposedto the photoresist 28 during the etch process, the harder it becomes toeffectively remove all of the residue 29 from the surface of the secondmetal layer 36. This is due to the fact that the organic materialsbecome metallized, as described previously. Thus, the structureillustrated in FIG. 1J is exposed to the cleaning composition of thisinvention after the oxygen ash step. The exposure time needed foreffectively cleaning the metallized organic residue 29 varies. Theexposure time must be adjusted to allow for adequate cleaning withoutremoving excess metal from underlying surfaces. As one example, anexposure time of about 90 seconds seems to provide an adequate balancebetween these two competing factors, when using concentrations of about5% by volume of phosphoric acid along with about 10% by volume of aceticacid and temperatures of about 30 to about 45 degrees Celsius.

If the multilevel interconnect structure includes more than two levelsof metal, subsequent insulating layers, vias, and metal layers areformed thereon, as described previously and represented generally as 38in FIG. 1K. The intermediate structures are cleaned in the phosphoricacid/acetic acid composition of the present invention, as describedpreviously. However, not every surface clean must be performed with thecleaning composition of the present invention, but it is advantageous todo so for achieving optimum electrical performance. The present cleaningcomposition may be used for one or more of the cleans when forming amultilevel interconnect structure.

The chemical composition of the present invention effectively removesmetallized organic residue from metal surfaces, without deleteriouslyremoving too much of the metal surface. By removing such residue,resulting resistivity of an IC is lowered. This is critical for thecontinued increase in device density, enabling fabrication of faster ICswith lower power consumption. Furthermore, due to the absence of strongorganic solvents in the dilute chemical composition, use of the cleaneris even more desirable because it doesn't require special hazardouswaste disposal procedures.

EXAMPLE

Twenty-five wafers, each having two different sized vias and patternedaluminum lines were prepared by forming patterned lower level aluminumlines on a substrate assembly surface, forming TEOS on the aluminumlines, patterning the TEOS using a photoresist to define the vias,etching the vias to the lower level aluminum lines using a fluorineplasma dry etch (including CF₄ and CHF₃), removing photoresist using anoxygen ash, and cleaning the vias using the cleaning compositions givenbelow in Table 1. Thereafter, the vias are filled with aluminum andupper level aluminum lines are formed by defining the upper levelaluminum lines in a layer of aluminum using photoresist, etching theupper level aluminum lines using a chlorine plasma dry etch (includingCl₂ and BCl₃), removing the photoresist using an oxygen ash, and thencleaning the upper level aluminum lines using the cleaning compositionsgiven below in Table 1. The vias of the first type had dimensions ofabout 0.6 microns with the vias of the second type having dimensions ofabout 0.48 microns. The upper level aluminum lines are of a thickness ofabout 6000 Å.

The wafers were grouped into lots of five. Each lot of five wafers wereimmersed in a dilute composition having the concentrations given belowin Table 1 for a process time also given in Table 1. The acetic acidconcentrations are in volume percent. The acetic acid was added to anexisting mixture of 5% phosphoric acid in deionized water. Theresistance values of the vias and patterned metal lines were measuredafter the clean was performed. Each wafer had fifty probe points usedfor each resistance determined, i.e,. fifty probe points for the via ofthe first type, fifty for the via of the second type, etc. In all casesthe resistance values are optimum when they are at the lowest meanvalues and have the lowest standard deviation. As shown below in Table1, the best dilute composition for via cleaning resulting from thisExample would be the composition including the 25% acetic acidconcentration with the wafer immersed for about 30 seconds. The bestdilute composition for cleaning surfaces having exposed patterned metalwould be the composition having the 10% acetic acid concentration withthe wafer immersed for about 90 seconds.

TABLE 1 Acetic Acid % Process First Via Second Via Pattered by vol TimeType Type Metal Line  5% 90 mean: 42.522 mean: 117.195 mean: 1090.135seconds std. dev.: 6.978 std. dev.: 26.797 std. dev.: 13.803 10% 90mean: 41.171 mean: 112.608 mean: 1060.995 seconds std. dev.: 6.408 std.dev.: 26.124 std. dev.: 4.422 25% 90 mean: 36.076 mean: 89.017 mean:1089.61 seconds std. dev.: 6.001 std. dev.: 20.695 std. dev.: 19.631 25%30 mean: 27.564 mean: 60.734 mean: 1112.307 seconds std. dev.: 1.405std. dev.: 16.436 std. dev.: 32.365  0% 90 mean: 31.151 mean: 69.929mean: 1113.156 seconds std. dev.: 5.692 std. dev.: 35.76 std. dev.:19.699

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. For example, the chemical cleaning composition of thisinvention is particularly useful wherever a metal surface needs to becleaned during the fabrication process. The scope of the inventionshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled.

1. A cleaning composition for use in semiconductor integrated circuitfabrication, the cleaning composition consisting essentially of a diluteaqueous solution of phosphoric acid and acetic acid, wherein thephosphoric acid is of a concentration of about 5% by volume or less andthe acetic acid is of a concentration of about 30% by volume or less. 2.The cleaning composition of claim 1, wherein the phosphoric acid is of aconcentration of about 5% or less by volume and the acetic acid of aconcentration of about 10% or less by volume.
 3. The cleaningcomposition of claim 1, wherein the phosphoric acid is of aconcentration of about 5% or less by volume and the acetic acid is of aconcentration in the range of about 20% by volume to about 30% byvolume.
 4. A cleaning composition for use in semiconductor integratedcircuit fabrication comprising phosphoric acid and acetic acid, whereinthe composition includes phosphoric acid at a concentration of about X %by volume or less, where X is 5, and acetic acid at a concentration ofabout (100-X) % by volume or less, and wherein the composition isoperable to remove exposed metal from a surface at a removal rate ofless than about 200 Å/minute.
 5. The cleaning composition of claim 4,wherein the composition is a dilute composition, wherein the dilutecomposition includes phosphoric acid at a concentration of about 5% byvolume or less, acetic acid at a concentration of about 30% by volume orless, and deionized water.
 6. The cleaning composition of claim 5,wherein the dilute composition includes phosphoric acid at aconcentration of about 5% by volume or less, acetic acid at aconcentration of about 10% by volume or less, and deionized water. 7.The cleaning composition of claim 5, wherein the dilute compositionincludes phosphoric acid at a concentration of about 5% by volume orless, acetic acid at a concentration in the range of about 20% by volumeto about 30% by volume, and deionized water.